Had a head scratcher recently. 2012 Western Star 4900 blew the air line between the drier and the purge tank one night. This is a metal braid, rubber coated line with threaded fittings, just like a hyd. hose but had blown apart and was in two pieces. Found and fitted a new one next morning. Within thirty seconds the entire length of the line started smoking then burst into flames. Managed to kick it off with a boot before it damaged any thing else. Both drier and tank are securely bolted to the chassis rail. Turns out, the battery cable, which runs along the inside of the rail, had shorted out on a tank mounting strap which, somehow, remained insulated from the chassis. So the air line became a fusible link, of sorts, as the current looked for a path back to earth via the drier.
As soon as you said it started smoking that was the clue, I had one do it in the shop years back. Except it was the stainless discharge line off the compressor that turned red. Also had one-A 2002 Pete 379 that had a remote jump start mounted to the frame near the starter. I had just shut the engine off and it erupted into flames--I like battery quick disconnects. A grain commodity company hear about six years ago had one that did the same, burned the cab damn near off.
I have a ditch compactor I was scraping out for the engine. Before I tore it apart I decided to start it up. I hooked up the jumpers and the positive fell against a hydraulic hose and made it in to a glow plug in about 15 seconds I had my back turned. (The jump pack is 2 group 31 batterys with 4/0 cables
I s’pose I can only be grateful that the hose did act like a fuse or the same thing could have happened to us. As far as I could tell, the cable routing is as it left the factory… no alterations and all clamps still in place.
Sometimes the factory gets it wrong. Occasionally in congested areas, i will slit a piece of heater hose and install it over the live cables and zip tie it at several places to help prevent chafing. Rough road vibration and age causes all sorts of problems the factory engineers and bean counters ignore
In the case of stainless discharge line,, a starter had been changed, grounds from starter to frame had been left off. And ground at battery to frame was loose.
I remember a similar situation back in early 90s within a year of eachother. One was a Ford LNT the other was a Mack U model. Both of them had lost the little 10ga cab/chassis ground. Each one of them lit up the power steering hoses between gear box and pump. The Mack was a fun challenge since it was four 6s and everything was saturated with oil. The Ford, not so much fun. They must have discharged every fire extinguisher within the yard. I can almost taste it still.
The great MT40 with cheap solenoid contacts---starter stays engaged---cables get real hot--- a mess of oil inside frame from 8V71---and poof. All it takes is the right combination at the right time.